1. Field of the Invention
This invention relates to achieving fiber processing operations without significant loss of desired hydrophobicity in processed fiber or corresponding nonwoven webs and products through the use of lubricants. This invention relates to the processes of production of the fiber as well as to the resulting fibers and to products, including nonwoven material and items containing nonwoven material, produced from the fibers.
2. Background Information
Hydrophobic woven and nonwoven fibers and fabrics are widely used in both industrial and personal applications. In some applications, for example, in leg cuffs, waist bands and back sheets for diapers or other personal hygiene devices, hydrophobicity is desirable in order to manage the flow of liquids. Hydrophobic fabrics may also be made into sterilizable surgical garb, such as gowns or caps, to protect the patient, medical personnel and others. Other uses of woven and nonwoven hydrophobic fibers and fabrics may be readily ascertained by those of ordinary skill in the art.
While the manufacture of fiber, webs and corresponding nonwoven materials are well-known in the art, attempts to broadly apply such knowledge to produce products in the area of personal hygiene, such as catamenial devices, disposable diapers, incontinence pads and the like, have met with serious technical problems due to significant differences in required fiber-spinning and working characteristics as opposed to properties desired in the final products.
Such products generally must have a fluid-absorbent core, usually comprising one or more layers of absorbent material such as wood pulp, rayon, gauze, tissue and the like. In some cases, super-absorbent powders, such as polyacrylate salt, may be used. To protect a wearer's clothing and surrounding areas from stains or wetting by fluids already absorbed in such a core, a fluid-impervious barrier sheet is usually required. The absorbent device is usually positioned against the body of the user with hydrophilic material facing and contacting the body and the fluid-impervious barrier sheet positioned on the outside or opposite side. Hydrophobic waistbands and leg cuffs are used to control the fluid.
A particularly troublesome technical problem arises when a high degree of hydrophobicity is desired in a nonwoven component produced substantially from conventionally bonded webs of hydrophobic fiber, such as polyolefin-containing webs produced from staple fiber or through spin-bonding.
In general, untreated fiber quickly becomes unworkable due to friction and accumulated static charge generated during conventional spinning, crimping, cutting and/or carding operations. For this reason, the art has long recognized and used a variety of topically applied antistatic agents (antistats) and lubricants which impart hydrophilic properties to an extent sufficient to permit conventional fiber processing. In commercial use, however, such treatment frequently results in a final fiber, web or nonwoven product which is substantially more hydrophilic than desired. Further, because of the nature of commercial high-speed operations, and the somewhat unpredictable affinity of known lubricating and antistatic agents to individual fiber batches of the hydrophobic type, it is often very difficult to maintain adequate control over the wetting characteristics of the final nonwoven product.
Various materials are known for assisting the processing of fibers while rendering and/or maintaining the fiber hydrophobic. Schmalz, U.S. Pat. No. 4,938,832, and European Patent Application No. 486,158, incorporated by reference as if set forth in their entireties herein, describe fiber finish compositions containing at least one neutralized phosphoric acid ester having a lower alkyl group, such as a 1-8 carbon alkyl group, which functions as an antistat, in combination with polysiloxane lubricants. These fibers have excellent properties, particularly for manufacture of hydrophobic nonwoven fabrics for hygienic products such as diapers, adult incontinence and sanitary protection products.
Johnson et al., U.S. Pat. No. 5,403,426, incorporated by reference as if set forth in its entirety herein, describes a method of preparing hydrophobic fiber for processing inclusive of crimping, cutting, carding, compiling and bonding. The surface modifier comprises one or more of a class of water soluble compounds substantially free of lipophilic end groups and of low or limited surfactant properties. The finished staple fiber or nonwoven product exhibits good hydrophobic properties.
Harrington, U.S. Pat. No. 5,540,953, incorporated by reference as if set forth in its entirety herein, describes antistatic compositions useful in the preparation of hydrophobic fibers and nonwoven fabrics. One finish described therein comprises 1) at least one neutralized C.sub.3 -C.sub.12 alkyl or alkenyl phosphate alkali metal or alkali earth metal salt, and 2) a solubilizer. A second finish described therein comprises at least one neutralized phosphoric ester salt.
Thus, there is a need to produce thermally bondable fibers that can achieve superior cross-directional strength, elongation and toughness properties in combination with fabric uniformity, loftiness and softness. In particular, there is a need to obtain fibers that can produce nonwoven materials, especially carded, calendered fabrics with cross directional properties on the order of at least about 200 to 400 grams/inch, preferably greater than about 400 grams/inch, and as high as about 650 grams/inch or more, at speeds as high as about 500 ft/min, preferably as high as 700 to 800 ft/min, and even more preferably as high as about 980 ft/min (300 m/min). Further, the fabrics can have an elongation of about 50-200%, and toughness of about 200 to 700 g/in, preferably about 480-700 g/in for nonwoven fabrics having a basis weight of from about 10 g/yd.sup.2 to 50 g/yd.sup.2. Thus, it is preferred to have these strength properties at a basis weight of about 20 g/yd.sup.2, more preferably about 12 to 20 g/yd.sup.2.